The present invention relates to a lens installation in an optical device, and more particularly to a structure for installing a lens in an optical device in such a fashion that the lens is slidable in the direction of its optical axis.
In the prior arts, one of known lens unit of this type is a collimator lens unit employed in a laser beam scanning device.
Usually, the collimator lens unit comprise a cylindrical hollow holder, a lens holding member slidably coupled into the hollow holder, and a lens carried by the holding member.
The lens is seated at the inner surface of a flange formed at the front portion of the holding member by means of a ring member threadably coupled to the inner surface of the holding member, in such a fashion that the optical axis of the lens meets the axial center of the hollow holder.
Thus, by fitting the hollow holder to a main frame of a laser beam scanning device such that the axial center of the hollow holder meets the optical axis of the laser beam scanning device, the lens holding member and therefore the lens itself can slide along the optical axis.
With the above constitution, however, when the lens is assembled into the holding member, there is a tendency that the lens is inclined with respect to the axial center of the holder, which requires trouble-some and time-consuming fine adjustments of the lens disposition.